Remove the legacy export

[cccclai]

Summary:
As title, try to see if we can get rid of the legacy export

Rollback Plan:

Differential Revision: D77761473

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12218

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❌ 5 New Failures, 2 Cancelled Jobs

As of commit e2cc5b3 with merge base c778063 ():

NEW FAILURES - The following jobs have failed:

• Build Presets / apple (llm) / build (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1
• Build Presets / apple (macos) / build (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1
• Build Presets / apple (pybind) / build (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1
• Build Presets / linux (pybind, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-models-linux (mobilebert, portable, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-models-linux (mobilebert, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.

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This pull request was exported from Phabricator. Differential Revision: D77761473

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[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D77761473

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D77761473